package jdbc;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

/**
 * 执行聚合函数
 */
public class JDBCDemo7 {
    public static void main(String[] args) {
        //需求：查看1年级1班共多少人
        /*
        SELECT COUNT(*) count
        FROM student s,
        JOIN class c ON s.class_id = c.id
        WHERE c.name='1年级1班‘；
         */
        try (Connection conn = DBUtil.getConnection();){
            Statement state = conn.createStatement();
            String sql = "SELECT COUNT(*) count FROM student s JOIN class c ON c.id=s.class_id WHERE c.name='1年级1班'";
            ResultSet rs = state.executeQuery(sql);
            if(rs.next()){
                int count = rs.getInt("count");
                System.out.println("共"+count+"人");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}
